1. Field of the Invention
The present invention relates to an improved treatment of sludge which comprises biological aggregate or polyvalent metal hydroxide aggregate to improve filtering characteristics.
2. Disclosure of the Prior Art
Various drainage treatments have been required for preventing pollution of environments.
The microorganism treatment has become important to treat the drainages such as drainage containing organic material. The microorganism treatment has been widely applied for various treatment of industrial waste and for removement of nitrogen sources which cause nutritious water in lakes or red sea water.
The microorganism treatment has been considered to be remarkably advantageous and has been widely applied, however serious problem has been caused. The problem is the treatment of the proliferated microorganism. In the drainage treatment, the sludge caused by the proliferated microorganism treatment is called as excess sludge to be discharged out of the system.
The discharged sludge containing the microorganism is pasty and tacky material which has high water content and is dehydrated and burnt or used in the reclamation or for other purposes.
However, it has been difficult to dehydrate the sludge by a filtration etc. because of tackiness. Accordingly, the treatment has been unsatisfactory and the treated sludge contains relatively high water content and serious disadvantage has been found for the further treatment.
Various treatments have been proposed to improve the dehydration of the sludge by an addition of lime, ferric chloride, polyaluminum chloride, polymer coagulants etc. before the filtration.
However, the effects are not satisfactory and impart slight decrease of the load of the filter etc. or cause other troubles. The problem has not been satisfactorily dissolved.
On the other hand, the aggregration-neutralization method imparts remarkable effect for removing suspensions metal compounds, COD, BOD, etc. by a simple equipment and operation and accordingly, it has been widely applied for the water purification, drainage treatment or industrial drainage treatment, etc.
However, serious problem has been closed up on the aggregation-neutralization method. The problem is the treatment of the sludge in the aggregation-neutralization method.
Typical coagulants include aluminum type coagulants such as aluminum sulfate, polyaluminum chloride, sodium aluminate; and iron type coagulants such as ferric chloride, ferrous sulfate, etc. These metal compounds as the coagulant are precipitated as the metal hydroxide and are separated as the sludge. The industrial drainages contain various metal compounds such as compounds of Fe, Cu, Al, Sn, Zn, Ni, Cr, Ti, etc. In order to remove these metal compounds, the neutralization-precipitation method has been usually employed, and these compounds have been removed as the metal hydroxide precipitates in the form of sludge. Thus, the sludges are hydrated pasty materials in the form of aquocomplexes, etc. whereby the dehydration are not easily attained. Accordingly, it has been difficult to use the sludge in effective usage and to use the sludge in the reclamation.
In order to improve the disadvantages, the sludges have been treated to improve the dehydration properties as follows:
(1) to add lime or ferric chloride; PA1 (2) to filtrate it after heating under high pressure; PA1 (3) to filtrate it after dissolving the metal hydroxide with acid; PA1 (4) to filtrate it after adding a polymer coagulant; PA1 (5) to separate water by a special filter cloth; or PA1 (6) to filtrate it after freezing the hydrate and melting it.
These methods have certain disadvantages and have not been satisfactory on the cost and the post treatments.